1. Field of the Invention
The present invention relates to an energy analyzer for use in analyzing energy of charged particles emitted from or reflected by a solid material or the like.
2. Description of the Background Art
In a conventional surface analyzer, an electron beam or ion beam is irradiated onto a surface of a solid specimen, and energy of a particle reflected by or secondary emitted from the surface of the solid specimen is analyzed to measure elementary composition or crystal structure of the solid surface or electronic structure in the solid. In such a surface analyzer, the energy of the particle reflected by or secondary emitted from the solid surface can be accurately analyzed, and requires an energy analyzer having a high analyzing sensitivity.
In FIG. 1, there is shown a conventional 127.degree. energy analyzer 1 of a face-symmetric electrostatic prism type having 127.degree. deflection angle, for use most popularly in various applications. In the energy analyzer 1, a pair of inside and outside electrodes 2 and 3 is arranged in parallel with each other along an arcuate line, and forms an electrostatic field P between themselves. A pair of DC voltage sources 4 and 5 supplies DC voltages to the inside and outside electrodes 2 and 3, respectively. An entrance aperture plate 7 having a hole or aperture 6 in its center is mounted in the entrance side of the electrostatic field P, and an exit aperture plate 9 having a hole of aperture 8 in the center is mounted in the exit side of the electrostatic field P. A particle detector (P.D.) 10 such as a secondary electron multiplier tube is arranged in front of the aperture 8 of the exit plate 9 for catching a particle coming out of the aperture 8 of the exit plate 9. The entrance and exit plates 7 and 9 are usually made of a metallic material such as stainless steels or molybdenum and are held to a zero voltage of an intermediate voltage between the inside and outside electrodes 2 and 3.
The energy analyzer 1 described above is operated in order to analyze particle energy as follows. By using an electron gun 11, an electron beam is irradiated to the surface of a solid specimen 12, and particles such as an electron having a negative charge or the like are emitted from the surface of the solid specimen 12. In order to analyze energy of a particle having a negative charge such as an electron, positive and negative voltages are applied to the inside and outside electrodes 2 and 3, respectively. The particles emitted from the solid specimen 12 are entered the electrostatic field P between the inside and outside electrodes 2 and 3 through the aperture 6 of the entrance plate 7, and the particles are subjected to be deflected by the electrostatic field P. Only a particle or particles having the energy capable of passing through a central orbit of zero voltage can come out of the aperture 8 of the exit plate 9 and come in the particle detector 10. Hence, the presence and amount of such a particle or particles can be detected.
However, in this case, the following problems arise. That is, the entrance and exit plate 7 and 9 are made of a metallic material and are kept at the zero voltage or the intermediate voltage between the inside and outside electrodes 2 and 3. Thus, isoelectric lines 13 are so formed by the inside and outside electrodes 2 and 3 as to surround the inside and outside electrodes 2 and 3, as shown in FIG. 1. As apparent from FIG. 1, the fringing fields between the inside and outside electrodes 2 and 3 and the entrance and exit plates 7 and 9 are largely disturbed, with the result of reducing the energy resolving power. Further, due to the presence of the disturbed fringing fields, the exit plate 9 can be provided with only one aperture on the beam central orbit in the central portion of the exit plate 9. As a result, plural energy analyses can not be effected at the same time.
In FIGS. 2 to 4, there is shown conventional velocity analyzer, such as a Wien filter for use in a mass separation of charged particles or the like. In a conventional ion radiation system, an ion beam is irradiated to the surface of a solid specimen to carry out an ion implantation into the specimen or an improvement of the quality of the specimen surface, or an analysis of the specimen surface is effected by analyzing the particle or particles emitted from or reflected by the surface of the specimen. In this case, in order to increase the purity of the radiating ion, an ion mass separator is used in an ion beam transfer system. This ion mass separator is basically an ion velocity separator or selector. A sector magnet or a Wien filter is known as an ion mass separator. Since the Wien filter has a simple structure and is used without bending the ion beam, thus it can be applied in various ion irradiation apparatuses. The Wien filter is also called as an E x B mass separator, and effects an ion velocity separation by a uniform electrostatic field and a uniform magnetic field crossing each other at right angles.
As shown in FIG. 2, the Wien filter comprises a pair of magnet 33 arranged in parallel in opposite sides, for forming magnetic flux 32 in the direction perpendicular to a moving direction 31 of an ion coming into the Wien filter, and a pair of electrodes 35a and 35b arranged in parallel in opposite sides, for giving an electric field in the direction perpendicular to the the moving direction 31 and the magnetic flux 32.
In this case, when an ion is entered the Wien filter, an ion having a velocity Vo satisfying a formula Vo=E/B, wherein E is an intensity of an electric field and B is a magnetic flux density, can go straight on in a space surrounded by the magnets 33 and the electrodes 35a and 35b without receiving any deflection. However, ions having a velocity except the velocity Vo are bent in the direction of the electric field 34 in FIG. 2, thereby effecting the ion velocity separation. In this case, when ions having the same energy are radiated from an ion source, the mass of the ions is separated.
In this Wien filter, the pair of magnets 33 are composed of a metallic material and are held to the zero voltage of an intermediate voltage between the electrodes 35a and 35b. Accordingly, isoelectric lines 36 in the space within the Wien filter are bent and disturbed, as shown in FIG. 3. Within the space surrounded by the magnets 33 and the electrodes 35a and 35b, the electric field directing perpendicular to the moving direction 31 of the ion and the magnetic flux 32 is given in the vertical center between the electrodes 35a and 35b. However, the electric field directing from the electrodes 35a and 35b to the magnets 33 is formed in the magnet sides, which is contrary to the condition such as a uniform electrostatic field required to the Wien filter, resulting in lowering the mass resolving power.
In order to avoid this problem, a pair of electrodes 35c and 35d having a U-shape longitudinal cross section is provided instead of the straight electrodes 35a and 35b to obtain a uniform electric field, as shown in FIG. 4. However, in this case, the uniform electric field portion or space is reduced, and hence the entire space within the Wien filter can not be effecitvely and advantageously utilized. Furthermore, there is a possibility or risk of bringing about enlarging of the whole system.